The present invention relates to an exchange or swap gate in a magnetic bubble memory with ion-implanted patterns. It also relates to a serial-parallel magnetic bubble memory having at least one of the said exchange or swap gates.
The invention particularly applies to the storage of binary information or bits, materialized in the form of isolated magnetic domains, called bubbles. These generally cylindrical domains have a magnetization which is the reverse of that of the remainder of the magnetic material (garnet) constituting the layer in which said domains are formed. In this memory, the duplication of the magnetic bubbles makes it possible to carry out bit by bit or bit block duplication.
In a monocrystalline magnetic layer, such as a magnetic garnet film, supported by an amagnetic monocrystalline garnet, the magnetic bubbles or domains are stable by applying a continuous magnetic field Hp perpendicular to the plane of the magnetic layer. In practice, this magnetic field is produced by a permanent magnet, thus ensuring the nonvolatility of the information contained in the memory.
In a magnetic bubble memory the bubbles are displaced by applying a rotary continuous or d.c. field H.sub.T in a direction parallel to the surface of the magnetic layer. The bubbles are displaced around so-called propagation patterns, defined in the upper part of the magnetic layer.
These patterns are shaped like disks, lozenges, triangles, T's, etc and can be made from a material based on iron and nickel, or can be obtained by implanting ions in the upper part of the magnetic layer through a mask making it possible to define the shape of said patterns. In the latter case, although ion implantation only takes place around the pattern, the latter are also called ion-implanted patterns. The propagation patterns are generally contiguous and, as a result of their shape, two adjacent patterns define two cavities or hollows between them.
The movement of the bubbles along these patterns generally takes place over a period of time equal to one third of the rotation period of the planar magnetic field H.sub.T, the bubbles remaining stationary in the cavity defined between two adjacent patterns throughout the remainder of the cycle. These cavities constitute so-called stable positions. In this way, shift registers are formed, in which the binary information 1 is represented by the presence of a bubble and binary information 0 by the absence of a bubble.
Apart from these propagation patterns, it is necessary to use electrical conductors for carrying out the following functions in the bubble memories writing: information recording, non-destructive reading, register-to-register transfer and erase.
One of the main known magnetic bubble memory types comprises a system of minor loops or registers used for storing information, associated with one or two major loops or registers constituting the memory access stations. The minor loops are arranged in longitudinally juxtaposed manner and the major loops are oriented perpendicularly to the minor loops. The magnetic bubbles are located in the minor loops and can be transferred into the major loops and vice versa, by means of unidirectional or bidirectional transfer gates.
When a single major loop is used, the reading and writing of the information takes place by means of said single loop. In the first case, reference is made to a memory having a major--minor organisation. However, when using two major loops, the information is written by means of one of these loops and the reading of the information by the other loop. These major loops are generally located on either side of minor loops. In the later case with two loops, reference is generally made to a memory having a serial-parallel organisation.
In the aforementioned bubble memories the production of a bubble on a major loop, corresponding to the writing of information, is carried out by applying a high current to a generally U-shaped conductor traversing the propagation patterns constituting the major loop. This operation, which is generally called nucleation, is carried out when the bubble is in a cavity defined between two adjacent patterns.
After nucleation, the bubble is then propagated, by applying rotary field H.sub.T to the major loop to the transfer gates in order to transfer the bubble from the major loop to a minor loop. These transfer gates are generally constituted by a U-shaped conductor traversing the patterns forming the minor loop. The application of a current pulse to said conductor makes it possible to extend each bubble between the tops of the propagation patterns of the major loop and those corresponding to the minor loop and then, the stopping of the current pulse leads to the contraction of the bubbles on the minor loop. Transfer is then realised. Thus, the information is stored on the minor loop.
The reading of this information takes place by transferring a magnetic bubble from a minor loop to a major loop, transfer taking place in the manner described hereinbefore.
In order to read an information in a non-destructive manner, the corresponding bubble must be duplicated. In the case of a bubble-by-bubble duplication, this is carried out by means of a conductor traversing the major loop, to which is applied a current pulse, leading to the elongation of the bubble on either side of the propagation path, followed by the splitting of said bubble into two. Thus, one of these bubbles, transferred on a detection path, can be destructively detected by a magnetoresistive detector, generally based on iron and nickel, whereas the other bubble is reinjected into the minor loop at the location occupied by the original bubble.
A swap gate, like that according to the invention, makes it possible to replace one information by another in a loop of a bubble memory. These swap gates are mainly used for writing an information into a minor loop by the transfer of said information from the major writing loop to the said minor loop. However, this swap gate can obviously be used in any random part of a bubble memory whenever one information has to be replaced by another.
A swap gate for a bubble memory with ion-implanted patterns is described in U.S. Pat. No. 4,394,746 filed on Dec. 16, 1981 and entitled "Swap gate for ion-implanted contiguous disk bubble devices". FIG. 1 shows a swap gate according to the teaching of this patent. FIG. 2 illustrates the operation of this swap gate.
FIG. 1 shows folded minor loops 2, a major loop 4 and exchange or swap elements 6, positioned between the major loop and the folded terminal part of the minor loop. Each swap element 6 has a first part 8 for swapping bubbles with the major loop, a second part 10 for receiving the bubbles from a first region 12 of the folded part of the minor loop 2 and a third part 14 for transferring the bubbles from the first part 8 to a second region 16 of the folded part of the minor loop 2. A pattern 18 is arranged between the first region 12 and the second region 16 of the minor loop 2 for forming two storage positions of the bubbles in the minor loop 2.
A first conductor 18 is also arranged between the major loop and the first part 8 of the exchange or swap element for forming a first transfer gate. A second conductor 20 is also positioned between the second part 10 of the swap element and the first region 12 of the minor loop, in order to form a second transfer gate. Finally, the third part 14 of the swap element is arranged so as to form a joining element with the second region 16 of the minor loop.
FIG. 2 is a larger scale view of a swap element positioned between a minor loop and the major loop. The dotted line arrows indicate the direction of movement of the magnetic bubbles along the ion-implanted patterns. It is possible to see the successive positions of a magnetic bubble 22 to be transferred to the major loop and a magnetic bubble 24 to be transferred to the minor loop, as a function of the phases of the rotary field H.sub.T numbered 1, 2, 3, 4. Letters a, b, c, d designated the successive rotations of rotary field, H.sub.T. Letters a', b', c', d' have the same meaning. For reasons of clarity, the electrical conductors are not shown.
Magnetic bubble 22 is replaced by magnetic bubble 24 in the minor loop in the following way. During the first rotation of field H.sub.T, the magnetic bubble 24 is moved along the major loop 4 and is transferred to the first part 8 of the swap element 6 by an adequate current pulse on the transfer conductor. During this time, bubble 22 is displaced on minor loop 2 and reaches the first region 12.
During the first half of the second rotation b of rotary field H.sub.T, said bubble is transferred to the second region 10 of swap element 6. It is then propagated along said pattern in the clockwise direction until it reaches the first part 8 of the exchange element at the start of the fourth rotation d of rotary field H.sub.T.
In the same way, during the second rotation B' and the first half of the third rotation c' of rotary field H.sub.T, bubble 24 moves along the swap element 6 to reach the third part 14. In the second half of said third rotation c', the said bubble is transferred to the second part 16 of minor loop 2. Thus, at time d'1, magnetic bubble 24 occupies the position which would have been occupied by bubble 22 if it had been propagated along the minor loop 2. The replacement of bubble 22 by bubble 24 is consequently completed. However, it remains necessary to transfer bubble 22 into position d1 on the major loop by a current pulse on the transfer conductor, followed by passing the said bubble to an annihilator located at the end of the major loop 4.
The swap gate described hereinbefore illustrates a recent prior art. In this swap gate, as in the other known swap gates, formed both in ion-implanted patterns and in a magnetic alloy of the iron--nickel type, the writing of an information into a minor loop always takes place by a double transfer between the minor loop and the major loop, the information to be erased being transferred to the major loop for destruction in an annihilator.
The swap gate according to the invention is based on a different principle. In this, transfer solely takes place from the major loop to the minor loop for supplying the new information to be stored. In the swap gate according to the invention, the information to be erased is not transferred to the major loop and is instead directly destroyed on the minor loop.
This more particularly makes it possible to eliminate the swap element and consequently to simplify the construction of the swap gates, whilst it also makes it possible to carry out said transfer more quickly, i.e. in a smaller number of cycles of rotary field H.sub.T.